1. Field of the Invention
The invention relates to an image forming apparatus, and particularly is suitable for application to an image forming apparatus such as an electrophotographic copying machine, a printer, a word processor or a facsimile apparatus for forming an image on a recording medium.
2. Description of Related Art
The construction of a laser beam printer as an example of an image forming apparatus adopting an electrophotographic process or other recording process according to the conventional art is shown in FIGS. 4 and 5 of the accompanying drawings.
In the laser beam printer according to the conventional art, there are a case where the conveying path of a recording material leading from sheet feeding means to fixing means via transferring means is set substantially horizontally as shown in FIG. 4, and a case where it is set obliquely as shown in FIG. 5.
That is, in the laser beam printer shown in FIG. 4, a sheet supply cassette 101 on which recording materials are placed and a sheet feeding roller 102 as sheet feeding means are provided on one end side of the apparatus.
Also, a transferring roller 103 as transferring means is provided in the central portion of the apparatus, and a fixing device 104 as fixing means is disposed on the other end side of the apparatus.
Also, a process cartridge 105 as image forming means and a laser scanner 106 as a light source are disposed above a conveying surface for the recording material P. This laser scanner 106 as the light source is comprised of a polygon mirror 106a and a turn-back mirror 106a. 
Further, conveying rollers 107a and 107b are disposed on the downstream side of the sheet feeding roller 102, and are designed to convey the recording material to the nip part between the transferring roller 103 and a photosensitive drum 108.
Also, the recording material P having passed through the nip part between the transferring roller 103 and the photosensitive drum 108 has an image thereon fixing in the fixing device 104, and thereafter is delivered onto a sheet delivery tray 110 through the nip part of a pair of sheet delivery rollers 109.
The feeding of the recording material P, the transfer of a visualized image (toner image) to the recording material P, and the heating and fixing of the visualized image on the recording material P are successively performed by the above-described process cartridge 105, the laser scanner 106, etc.
Such a printer, if its downsizing is contrived, is decreased in the volume of the printer itself and is reduced in heat capacity. Therefore, the temperature rise in the apparatus becomes remarkable by the heat of the fixing means which is a heat generating member.
So, some downsized printers include products adopting a construction in which the fixing means which is a heat source is disposed in the upper portion of the printer so that heat exhaust efficiency may become high. Such a product is shown in FIG. 5.
As shown in FIG. 5, in such image forming apparatus, a sheet supply cassette 201 as a sheet supply portion and a sheet feeding roller 202 as sheet feeding means are provided on the lower side thereof, a transferring roller 203 as transferring means is provided in the central portion thereof, and a fixing device 204 as fixing means is provided on the upper side thereof.
Also, louvers are provided on the upper side and sides of outer packaging 205 covering the fixing device 204, whereby the heat generated by the fixing device 204 can be efficiently delivered out of the apparatus.
A process cartridge 206 as image forming means and a laser scanner 207 as optical means having a polygon mirror 207a and a turn-back mirror 207b are disposed substantially at the same height or below the fixing device 204 as the fixing means, and the feeding of the recording material P, the transfer of the visualized image to the recording material P, and the heating and fixing of the visualized image on the recording material P are successively performed.
The recording material P after having had the image thereon fixed by the fixing device 204 passes along a curved discharge guide, whereby it assumes a posture in which the printed surface thereof faces down, and is discharged onto a sheet discharge tray 209 by a pair of sheet discharging rollers 208. In the image forming apparatus shown in FIG. 5, conveying rollers 210a, 210b and a photosensitive drum 211 are provided on the downstream side of the sheet feeding roller 202, and a motor 212 is further provided.
Also, in Japanese Patent Application Laid-Open No. 2001-337499, there is disclosed a construction in which a recording material is upwardly delivered from a fixing device, is guided by a curved delivery guide and is delivered out of an apparatus main body.
In the printer as described above, a higher speed is always desired. Particularly, to shorten the time required to output the first sheet (the first print-out time), it is effective to shorten the conveying path from the feeding to the discharge of the recording material.
In the image forming apparatuses according to the conventional art shown in FIGS. 4 and 5, the sheet delivery tray is disposed at an acute angle with respect to the conveying path. Therefore, the recording material P after having passed through the fixing means is delivered onto the sheet delivery tray along the curved discharge guide with its print surface facing down.
Therefore, when an attempt is made to shorten the sheet delivery guide, the radius of curvature thereof must be made small. However, when the sheet delivery guide is constructed with a small radius of curvature, there is the evil that the frictional sound caused by the pass of the recording material becomes great or the recording material becomes liable to be caught by the sheet delivery guide.
Therefore, the sheet delivery guide after the image on the recording material has been fixed by the fixing means must be constructed with a gentle radius, and it has been difficult to shorten the conveying path by shortening the sheet delivery guide. Also, in the technique disclosed in Japanese Patent Application Laid-Open No. 2001-337499, the sheet delivery guide downstream of the fixing apparatus is of a curved shape and therefore, in order to prevent the recording material from being caught by the sheet delivery guide, it is necessary to make the radius curvature great. This has led to the problem that the recording material having had the image thereon fixed requires a long time until it enters a pair of sheet discharge rollers, and the first print-out time becomes long. Also, as the downsizing of the printer progresses, it is necessary to make the spacing among the constituents such as the sheet feeding means, the fixing means and the process cartridge, a minimum necessary space such as the conveying path for the recording material or the mounting and dismounting locus of the process cartridge and the outer packaging of the product as short as possible.